linux-kernel - [PATCH 3.18 006/120] gso_segment: Reset skb->mac

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Message-Id: <20181011152549.779181670@linuxfoundation.org>
Date:   Thu, 11 Oct 2018 17:33:07 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Dave Taht <dave.taht@...il.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Toke Høiland-Jørgensen <toke@...e.dk>,
        "David S. Miller" <davem@...emloft.net>
Subject: [PATCH 3.18 006/120] gso_segment: Reset skb->mac_len after modifying network header

3.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Toke Høiland-Jørgensen <toke@...e.dk>

[ Upstream commit c56cae23c6b167acc68043c683c4573b80cbcc2c ]

When splitting a GSO segment that consists of encapsulated packets, the
skb->mac_len of the segments can end up being set wrong, causing packet
drops in particular when using act_mirred and ifb interfaces in
combination with a qdisc that splits GSO packets.

This happens because at the time skb_segment() is called, network_header
will point to the inner header, throwing off the calculation in
skb_reset_mac_len(). The network_header is subsequently adjust by the
outer IP gso_segment handlers, but they don't set the mac_len.

Fix this by adding skb_reset_mac_len() calls to both the IPv4 and IPv6
gso_segment handlers, after they modify the network_header.

Many thanks to Eric Dumazet for his help in identifying the cause of
the bug.

Acked-by: Dave Taht <dave.taht@...il.com>
Reviewed-by: Eric Dumazet <edumazet@...gle.com>
Signed-off-by: Toke Høiland-Jørgensen <toke@...e.dk>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 net/ipv4/af_inet.c     |    1 +
 net/ipv6/ip6_offload.c |    1 +
 2 files changed, 2 insertions(+)

--- a/net/ipv4/af_inet.c
+++ b/net/ipv4/af_inet.c
@@ -1288,6 +1288,7 @@ static struct sk_buff *inet_gso_segment(
 		if (encap)
 			skb_reset_inner_headers(skb);
 		skb->network_header = (u8 *)iph - skb->head;
+		skb_reset_mac_len(skb);
 	} while ((skb = skb->next));

 out:
--- a/net/ipv6/ip6_offload.c
+++ b/net/ipv6/ip6_offload.c
@@ -118,6 +118,7 @@ static struct sk_buff *ipv6_gso_segment(
 		ipv6h = (struct ipv6hdr *)(skb_mac_header(skb) + nhoff);
 		ipv6h->payload_len = htons(skb->len - nhoff - sizeof(*ipv6h));
 		skb->network_header = (u8 *)ipv6h - skb->head;
+		skb_reset_mac_len(skb);

 		if (udpfrag) {
 			int err = ip6_find_1stfragopt(skb, &prevhdr);